TWO TYPES OF TRAITS

TWO TYPES OF TRAITS

Discrete or discontinuous traits: traits occur in distinct Categories: Trait is there or it is not (examples: albinism, cystic fibrosis, Huntington's disease) Mendelian inheritance, single genes, dominance, recessiveness

Continuous traits: Distribution of phenotypes in the population varies along a continuum. Individuals differ by small degrees. (examples include height, blood pressure, reaction time, learning ability) Polygenic quantitative or multifactorial inheritance. Genes act additively.

INHERITANCE OF CONTINUOUS TRAITS

A simple case with two loci, two alleles each

A A1

B B1

An allele with a prime 1, adds one unit of measure to the phenotype

If a trait, say height, is controlled by two loci, A and B, and each locus has two alleles, one regular and one prime allele, what are the possible genotypes and phenotypes?

AABB 0----------short AA1BB 1----------semi-short AABB1 1----------semi-short AA1BB1 2----------average A1A1BB 2----------average AAB1B1 2----------average A1A1B1B 3----------semi-tall A1AB1B1 3----------semi-tall A1A1B1B1 4----------tall

semi-

semi-

short short average tall

tall

AABB AA1BB AA1BB1 A1A1B1B A1A1B1B1 AABB1 A1A1BB A1AB1B1 AAB1B1

0

1

2

3

4

Two loci, Two alleles

Three loci, Two alleles

 ................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download